In the fabrication of semiconductor devices, it is increasingly important to precisely control the uniformity of thickness of coated layers. Uniformity in the thickness of coated layers can increase yield, improve the performance of individual semiconductor devices and may allow the devices across the wafer to more consistently meet a particular specification. When semiconductor wafers are coated by sputter coating, a material is sputtered off of a target cathode in such a manner that it deposits on the surface to be coated. See generally, R. W. Berry, et al., Thin Film Technology, (1968) and L. J. Maissel, et al., Handbook of Thin Film Technology, (1970). Such sputter coated films, for example, of aluminum, are employed for the metallization of integrated circuits. Heretofore, uneven films have either been tolerated or attempts have been made to shape the sputtering cathode or to arrange the geometry of the system in order to deposit as uniform a film as possible.
The conventional technique for contouring the thickness of the coating in a sputter deposited layer is to interpose a blocking shield inbetween the cathode target and the substrate. As disclosed in C. H. George, "Apparatus for Feeding and Coating Masses of Workpieces in a Controlled Atmosphere", U.S. Pat. No. 3,856,654, a fixed blocking shield may be inserted between a cathode target and a substrate. When the sputter coating from such a work station is combined with coating from unshielded stations, then a more uniform overall film may be obtained. Or, as disclosed in A. M. Hanfmann, "Depositing Material on a Substrate Using a Shield", U.S. Pat. No. 3,904,503, an arbitrarily shaped planar member is inserted between a cathode target and a source as the substrate moves linearly past or around the source. The shape of the edge of the planar member is selected to match the thickness contours of the substrate coated in the system without a shield. Thus, the inherent non-uniformities introduced by the system may be compensated. In both cases, since no shuttering is used, there is a leading edge and a trailing edge to the deposition as the substrate moves past the cathode. Also, due to the fact that either the substrate or the shield moves, and since the relative movement is essentially linear, it is not possible to produce contouring having asymmetry derived from the unique circular symmetry of a semiconductor wafer.
Every process practiced in the semiconductor industry has an inherent nonuniformity, a signature that reflects its configuration and the character of the process. In order to produce a process result that in the aggregate is uniform, then, it is necessary at times to deliberately introduce nonuniformities in one process step to compensate for the signature of a preceding or following process step. Alternately, in order to produce a process result that in the aggregate possesses a desired thickness contour, it is also necessary to deliberately introduce a nonuniformity in one process step to compensate for the signatures of other process steps and thereby produce, in the aggregate, the desired thickness contour. The conventional approaches described above may affect such compensation if the system or substrate configurations are symmetric but do not readily permit asymmetric compensation, especially asymmetric compensation derived from the essentially circular symmetry of semiconductor wafers.
Apparatus which may affect compensation for process step signatures generally in sputter deposited films and is suited for asymmetric compensation is disclosed in the copending application Ser. No. 325,588, of D. Harra, et. al., "Improved Blocking Shield and Method for Contouring the Thickness of Sputter Coated Layers", filed on even data herewith. The method described therein is particularly suited for producing compensation when the circular symmetry of semiconductor wafers is involved. It would be desirable to adapt such apparatus to produce asymmetric compensation, particularly compensation based on asymmetrics derived from the circular symmetry of semiconductor wafers.